The nova acted as a rendezvous signal, causing all starlines connected to that star to flare up. Otherwise it's too hard to find aliens - opening starlines is expensive. It's the chance of a direct encounter (small) versus chance of at least one mutual neighbor (larger).
Even so, for reasons of which you are very well aware, meeting two sets of aliens should be a lot less likely than meeting one set, so we ought to take that in account when we are trying to make sense of what is going on. But I accept that positing a minor god is rather a primitive reaction, especially as we already know that in your impossible possible world no Singularity is reachable by any means currently envisaged.
If human evolution has really been speeding up over the last ten-thousand years, as Greg Cochran believes, does it necessarily make sense to say that we are no longer in the EEA? Perhaps modern humans are better adapted to modern life than the "caveman" thesis (or just-so story?) suggests.